16,681 research outputs found
Spinning Relativistic Particle in an External Electromagnetic Field
The Hamiltonian formulation of the motion of a spinning relativistic particle
in an external electromagnetic field is considered. The approach is based on
the introduction of new coordinates and their conjugated momenta to describe
the spin degrees of freedom together with an appropriate set of constraints in
the Dirac formulation. For particles with gyromagnetic ratio , the
equations of motion do not predict any deviation from the standard Lorentz
force, while for an additional force, which corresponds to the
magnetic dipole force, is obtained.Comment: Latex file, 11 page
Estimating the magnetic field strength from magnetograms
A properly calibrated longitudinal magnetograph is an instrument that
measures circular polarization and gives an estimation of the magnetic flux
density in each observed resolution element. This usually constitutes a lower
bound of the field strength in the resolution element, given that it can be
made arbitrarily large as long as it occupies a proportionally smaller area of
the resolution element and/or becomes more transversal to the observer and
still produce the same magnetic signal. Yet, we know that arbitrarily stronger
fields are less likely --hG fields are more probable than kG fields, with
fields above several kG virtually absent-- and we may even have partial
information about its angular distribution. Based on a set of sensible
considerations, we derive simple formulae based on a Bayesian analysis to give
an improved estimation of the magnetic field strength for magnetographs.Comment: 8 pages, 7 figures, accepted for publication in A&
Estimating the Effects of U.S. Distortions in the Ethanol Market Using a Partial Equilibrium Trade Model
In this paper we assess the impact of the elimination of trade distortions on imports from Brazil to the U.S. For this purpose, we estimate a partial equilibrium trade model an ethanol export supply function for Brazil and an ethanol import demand function for the U.S.-, based on annual data from 1975 to 2006, and use the results to compute a back-of-the-envelope measure of the deadweight loss derived from those trade distortions as well as one derived from producing the 35 billion gallons proposed in the Twenty in Ten 2007 State of the Union Policy Initiative assuming the distortions are not eliminated. Two-stage least squares is used to estimate both functions, the world price of ethanol being treated as endogenous. This paper supports the idea that the U.S. and Brazil would reap gains from trade if trade distortions were eliminated.Resource /Energy Economics and Policy,
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
Near-IR internetwork spectro-polarimetry at different heliocentric angles
The analysis of near infrared spectropolarimetric data at the internetwork at
different regions on the solar surface could offer constraints to reject
current modeling of these quiet areas.
We present spectro-polarimetric observations of very quiet regions for
different values of the heliocentric angle for the Fe I lines at 1.56 micron,
from disc centre to positions close to the limb. The spatial resolution of the
data is 0.7-1". We analyze direct observable properties of the Stokes profiles
as the amplitude of circular and linear polarization as well as the total
degree of polarization. Also the area and amplitude asymmetries are studied.
We do not find any significant variation of the properties of the
polarimetric signals with the heliocentric angle. This means that the magnetism
of the solar internetwork remains the same regardless of the position on the
solar disc. This observational fact discards the possibility of modeling the
internetwork as a Network-like scenario. The magnetic elements of internetwork
areas seem to be isotropically distributed when observed at our spatial
resolution.Comment: Sorry, this is the version with the correct bibliography. Some
figures had to be compressed. Accepted for publication in A&
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
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